Hydrogen peroxide is an important intermediate chemical useful in such applications as water treatment, pulp and paper bleaching, and organic synthesis. At present, the commercial process for producing hydrogen peroxide involves anthraquinone autooxidation (see, e.g., U.S. Pat. Nos. 4,428,923 and 6,524,547). The process requires numerous reaction and purification sections, uses a large volume of solvent, and provides a less-than-ideal yield of hydrogen peroxide.
Hydrogen peroxide can also be made by a direct reaction of hydrogen and oxygen in the presence of a suitable catalyst. Known methods of making hydrogen peroxide from hydrogen and oxygen use supported transition metals (Group 3 to 12 elements), especially platinum group metals. A wide variety of inorganic and organic supports have been identified, including activated carbon (see, e.g., U.S. Pat. Nos. 6,168,775 and 6,649,140), fluorinated carbon (see, e.g., U.S. Pat. No. 5,846,898), sulfonic acid-functionalized carbon (see, e.g., U.S. Pat. No. 6,284,213), silica, alumina (see, e.g., U.S. Pat. No. 5,961,948), polymer fiber (see, e.g., U.S. Pat. No. 6,375,920), and ion-exchange resin (see, e.g., U.S. Appl. Pub. No. 2003/0215383).
Hydrogen peroxide is an attractive oxidizing agent in the chemical industry because water is the only byproduct. For example, the oxidation of alkanes, arenes, olefins with hydrogen peroxide in the presence of a titanium zeolite has been demonstrated (see New Developments in Selective Oxidation, G. Centi and F. Trifiro, Ed., pp. 33-38). Hydrogen peroxide solutions prepared from the reaction of hydrogen and oxygen may be used (see, e.g., U.S. Pat. Nos. 6,284,213 and 6,888,013; U.S. Appl. Pub. No. 2004/0151658).
Recently, a technique called “microencapsulation” was used to prepare catalysts with improved properties, as reviewed in recent publications (Chem. Commun. (2003) 449 and references cited therein; Angew. Chem., Int. Ed. 40 (2001) 3469; J. Am. Chem. Soc. 120 (1998) 2985; U.S. Appl. Pub. Nos. 2005/0201925, 2005/0202957, and 2005/0203304). EP 0 498 166 A1 discloses an alumina-supported Pd catalyst impregnated with 4-bromostyrene or styrene that is subsequently polymerized (see Example 7 and Comparative Example 8). The poly(4-bromostyrene)-coated catalyst is active in generating hydrogen peroxide from hydrogen and oxygen. U.S. Appl. Pub. No. 2004/0184983 describes a catalyst consisting of: (a) one or more metals of the platinum group as active components; (b) one or more polyolefins; and (c) a carrier. The polyolefin is dissolved in a solvent, and the resulting solution is used to impregnate the carrier or the catalyst. The catalyst is useful in producing hydrogen peroxide from hydrogen and oxygen in a reaction solvent containing halogenated and/or acid promoters.